1. Field of the Invention
The present invention relates to a wake turbulence detecting system detecting by means of laser radar deployed in an airport wake turbulence which appears behind main wings of an aircraft during takeoff or landing and continues to exist along the trail of the aircraft.
2. Description of the Background Art
Wake turbulence is a turbulence winding up vortexes rotating in opposite directions to each other, generated backward of right and left main wings of a flying aircraft. As for the scale of wake turbulence, a diameter of a vortex may extend to a few hundred feet, deteriorating the controllability of the following aircraft entering the trail. When wind is weak, wake turbulence continues to exist in consonance with a trail of an aircraft for a few minutes. Lifetime of the wake turbulence gets longer especially early in the morning when wind is slight and strong radiational cooling occurs. On the other hand, when wind is strong, the wake turbulence may spread, resulting in short lifetime but possible drift downstream from where it started, affecting aircraft flying in other sky areas. In consideration of existence of such wake turbulence, in main airports where many aircraft take off or land aircraft traffic control is carried out. Requests to shorten the time interval between takeoffs or landings are getting stronger to meet the increasing demand for air cargo delivery.
For such requests, laser radar for watching the wake turbulence may be installed in airports and when it is received that there is no wake turbulence the following aircraft can be allowed to take off or land by aircraft traffic control even though a few minutes have not yet passed after the takeoff or landing of preceding aircraft. FIG. 12 is a figure which shows an airport where a laser radar is deployed. In FIG. 12, reference number 30 denotes a runway. Reference number 31 denotes an aircraft. Reference number 32 denotes a wake turbulence generated backward of aircraft 31. Reference number 33 denotes a laser radar installed in the vicinities of a runway. In addition, FIG. 13 is a block diagram showing constitution of a conventional wake turbulence detecting system. In FIG. 13, reference number 34 denotes a scanning control part which generates scanning control signal for controlling the irradiating direction and the irradiating gun elevation of laser beam. Reference number 35 denotes a beam transmitter-receiver unit which emits a laser beam based on a scanning control signal and detects the reflected laser beam reflected by dust or particles in the atmosphere. Reference number 36 denotes a signal processing device which detects wake turbulence from a reflected laser beam via the beam transmitter-receiver unit. Reference number 37 denotes wake turbulence detecting part which detects wake turbulence from a reflected laser beam and generates wake turbulence information. Reference number 38 denotes a monitor display which displays the wake turbulence information generated by wake turbulence detecting part 37.
FIG. 14 is a block diagram which shows detailed constitution of beam transmitter-receiver unit 35. In FIG. 14, reference number 39 denotes a beam transmit-receive circuit which excites a laser and generates a reception signal including Doppler information indicating the behavior of dusts or solids in the atmosphere and the intensity of the received reflected laser beam. Reference number 40 denotes beam enlarge-reduce device, which enlarges the width of a laser beam from beam transmit-receive circuit 39 and reduces the width of a reflected laser beam.
Referring now to FIGS. 12, 13 and 14, operation of the wake turbulence detecting system is described. In FIG. 13, beam transmitter-receiver unit 35 composing laser radar 33 emits a laser beam toward the direction of runway 30, namely the flight course traced by aircraft 31 during takeoff. Scanning control part 34 outputs scanning control signal for changing the direction and the gun elevation angle of laser beam to beam transmitter-receiver unit 35, controlling the beam to scan over the predetermined irradiation area. The transmitted laser beam from beam transmitter-receiver unit 35 is reflected by aerosols such as dusts or solids. The reflected laser beam reflected by dusts or solids returns toward the laser radar and is received by beam transmitter-receiver unit 35. Beam transmitter-receiver unit 35 generates a reception signal including Doppler information indicating the behavior of dusts or solids in the atmosphere and the reception intensity information of the reflected signal indicating the intensity of the reflected laser beam and outputs them to wake turbulence detecting part 37 of signal processing device 36.
Wake turbulence detecting part 37, based on a reception signal transmitted by beam transmitter-receiver unit 35 of laser radar 33, detects the velocity and the direction of the wind at predetermined constant intervals (e.g. about 30 meters). Furthermore, wake turbulence detecting part 37, based on scanning control signal transmitted by scanning control part 34, detects the velocity and the direction of the wind for each direction the beam is pointed. In addition, wake turbulence detecting part 37, based on the velocity and the direction of the wind along beam transmitting direction and along that of each direction, finds the center position indicating the wake turbulence position, the diameter of a vortex indicating the scale of wake turbulence vortex, and the intensity of wake turbulence, then composing wake turbulence information. Furthermore, wake turbulence detecting part 37 generates display data for indicating the wake turbulence information on monitor display 38 and outputs them to monitor display 38. Monitor display 38 indicates wake turbulence information such as an outbreak position, a scale and intensity of the wake turbulence based on shown data. In addition, among devices composing a wake turbulence detecting system, laser radar 33 is arranged in the vicinities of runway 30 and signal processing device 36 and monitor 38 are installed inside the control tower.
In the control tower, control person in charge, based on wake turbulence information indicated on monitor display 38, confirms whether there is a wake turbulence or not. If it is confirmed that wake turbulence does not exist or has already disappeared, the control person in charge promptly directs the following aircraft to take off or land on without waiting for a few minutes defined as minimum time interval for takeoffs or landings of aircraft. Thus, the wake turbulence detecting system enables the control person in charge to watch the wake turbulence from its outbreak to its extinction so that aircraft control is made more efficient.
By the way, there remains a problem that should be solved to execute safer aircraft traffic control by means of a wake turbulence detecting system as mentioned above. For example, though the wake turbulence detecting system shows nonexistence of wake turbulence, if it is unclear whether wake turbulence really does not exist or exists but merely cannot be detected, highly trustworthy aircraft traffic control can not be afforded. Therefore, it desirable that there are no blind spots which disturb the detection of wake turbulence.
As described above, wake turbulence detecting system detects Doppler components from the behavior of dusts and solids floating in the atmosphere and so detects the direction and the velocity of wake turbulence vortex. In order to receive the Doppler components of the intensity (velocity) of the wake turbulence vortex efficiently, It is desirable to deploy the laser radar at a position where laser beam can be oriented in the direction parallel to the vortex direction. In other words, as shown in FIG. 7, laser radar 33 can observe wake turbulence 32 well when aircraft 31 is located on the point A. However, it becomes difficult to receive wake turbulence 32 when aircraft 31 changes the flight course after takeoff and arrives at the point B. Thus, the blind spot of the laser radar observing wake turbulence is determined in accordance with the position of the laser radar and the flight course that the aircraft traces.
The present invention is proposed to solve the aforementioned problem and it is an object of the present invention to provide a wake turbulence detecting system which makes it possible to reduce the blind spot in observing wake turbulence.
Wake turbulence detecting system according to the present invention comprises a first laser radar located close to a runway, said first laser radar including a laser transmitter-receiver unit emitting laser beam toward an aircraft taking off or landing on said runway and receiving reflected laser beam reflected back by the aerosol which is floating in the atmosphere that said laser beam irradiated and which scatters said laser beam, and a scanning control part controlling the irradiating direction of the laser beam from said laser transmitter-receiver unit; a second laser radar located at a position differing from that of said first laser radar, said second laser radar including a laser transmitter-receiver unit emitting laser beam toward an aircraft taking off or landing on said runway and receiving reflected laser beam reflected back by aerosol which is floating in the atmosphere that said laser beam irradiated and which scatters said laser beam, and a scanning control part controlling the irradiating direction of the laser beam emitted from said laser transmitter-receiver unit; and a signal processing device producing first wake turbulence information including the scale, the wind velocity and the birth place of the wake turbulence in the area where said first laser beam is irradiated, and producing second wake turbulence information including the scale, the wind velocity and the birth place of the wake turbulence in the area where said second laser beam is irradiated, and indicating the wake turbulence information of the area where the irradiation of said first and said second laser radar do not overlap each other by making a composite of said first and second wake turbulence information, and indicating the wake turbulence information of the area where the irradiation of said first and second laser radar overlap each other by comparing said first wake turbulence information with second wake turbulence information to select the one having a larger value.
Wake turbulence detecting system according to the present invention comprises a first laser radar located close to a runway, said first laser radar including a laser transmit-receive circuit which generates a laser beam irradiated to the atmosphere and which detects reflected laser beam reflected back by aerosol floating in the atmosphere, a beam enlarge-reduce device enlarging the width of laser beam output from said laser transmitter-receiver unit to adjust the irradiating direction of said laser beam and also reducing the width of said reflected laser beam, a laser transmitter-receiver unit having a beam isolator provided between said laser transmit-receive circuit and said beam enlarge-reduce device to switch the path of laser beam output from said laser transmitter-receiver unit, and a scanning control part producing scanning control signal to control the direction of laser beam output from said laser transmitter-receiver unit for controlling said beam enlarge-reduce device in response to said scanning control signal; second laser radar including a laser transmitter-receiver unit having beam enlarge-reduce device which enlarges the width of laser beam generated by said laser transmitter-receiver unit input after its path has been switched by said beam isolator and irradiates the laser beam to the atmosphere adjusting the irradiating direction and reduces the width of reflected laser beam to output it to laser transmit-receive circuit of said first laser radar, and a scanning control part producing scanning control signals to control irradiating direction of laser beam emitted by said laser transmitter-receiver unit and for controlling said beam enlarge-reduce device in response to said scanning control signal; a signal processing device producing wake turbulence information including the scale, the wind velocity and the position of the wake turbulence and producing indicating signal for indicating said wake turbulence information on monitor display; and a laser radar selecting part controlling said beam isolator based on aircraft position information and position information read from memory means storing blind spot information of said first and second laser beam and switching the source of the laser beam excited by said laser transmitter-receiver unit selectively between said first and second laser radar.